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Old 12th Nov 2017, 3:56 pm   #16
kalee20
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Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,061
Default Re: BRY39 - Solid state switches.

Quote:
Originally Posted by Diabolical Artificer View Post
Thanks chaps. I've found the basic relaxation osc circuit and a few other bits online for PUT's, but nothing specific for the BRY39. The 2N6027 comes up in searches for PUT's but this has no cathode gate. In the example for the 2N6027 here - http://www.circuitstoday.com/programmable-ujt there is an unused P region, does this mean the 39 has an extra N region which is the cathode gate?
The BRY39 is PNPN with a connection to every region. The 2N6027 just omits a connection to the inner P region.

I've used the cathode gate for connecting a resistor between here and cathode, to speed-up stored charge dissipation after it's been conducting. Otherwise you have to wait several microseconds before normal operation resumes. It's also useful for triggering the device 'on'.

Quote:
Originally Posted by Argus25 View Post
Rather than using a UJT or a PUT, I think its better to wire a PNP and NPN transistor together to make a PUT. This was done to create the vertical oscillator on one of my vintage computer monitors. Also I have a Conrac video monitor that uses a UJT as the vertical scan oscillator.

At least if the PUT is made from two common garden transistors, its easy to repair/replace it.
The trouble is, it is hard to find PNP transistors with a reverse Vbe of more than 5V, whereas the BRY39 does 60V (from memory). The internal PNP transistor is, as a result, low current gain, but that does not matter as thyristor action only requires the sum of the NPN and PNP alpha gains be greater than 1, and the internal NPN transistor has plenty of gain.

I've used the BRY39 twice in the 'day job,' once was as a start-up component in an off-line switch-mode power supply. A large resistor charged up a 470μF capacitor to about 20V (as determined by a Zener diode on the anode gate. The PUT then fired, dumping the charge into another capacitor on its cathode, connected to the SMPS control circuitry. The energy available powered the control circuitry long enough to start up, at which point an auxiliary secondary winding on the power transformer took over providing power.

The other application was a protection crowbar across a low-power 8V supply rail which powered a pressure transducer in a liquid oxygen tank. To stop self-heating, there was a requirement that the transducer be powered for 4 seconds maximum. This was defined by software, but in case the software crashed leaving power 'on,' I used a BRY39 and a few components to generate a 5second delay. If the supply rail hadn't been killed by then, the PUT fired and crowbarred it. I needed only the BRY39, a timing capacitor and resistor, the two programming resistors, and a small blocking diode. The whole thing was powered by the rail it was protecting (250μA current drain till it 'fires').

I'm also using it as the 'on' period timer in a small battery-to-HT&LT power supply for battery valve radios, one of which happens to be playing right now! This is where I needed the cathode-gate resistor. Varying the voltage on the anode-gate controls the period, allowing output voltage regulation. It works well, though I agree dedicated control IC's exist!

Last edited by kalee20; 12th Nov 2017 at 4:01 pm. Reason: Grammar
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